1. Field of the Invention
The present invention relates generally to exhaust nozzles for jet engines, and in particular to a jet-engine-exhaust nozzle that may be used on fixed or rotary wing aircraft, rockets, or missiles for optimizing take-off, climb and cruise performance, as well as for increasing flight safety and reducing speed at landing.
2. Description of Related Art
Thrust vectoring technology has been successfully demonstrated on tactical military aircraft to provide maneuvering advantages in very low speed, as well as very high angle-of-attack flight regimes. Current research is exploring the benefits of using thrust vectoring to decrease cruise trim drag under high altitude and mid to high speed conditions. This technology has matured to the extent that it is being incorporated into military fighter aircraft.
As far as is known, thrust vectoring has not been used on commercial or business aircraft. Some of the reasons for this are that the technology is typically very complex and involves many moving parts, which is detrimental to the overall dispatch reliability and operational cost of a business or commercial aircraft. Another reason that thrust vectoring has not been used on commercial or business aircraft is that these aircraft usually have little need for maneuvering agility. Despite the foregoing, the potential for improved safety and increased cruise efficiency that may result from the use of thrust vectoring would make it attractive to the commercial and business aircraft community if a simple thrust vectoring system having a low number of moving parts could be provided.
Thrust vectoring could provide benefit to commercial and business aircraft by providing improved longitudinal stability. Longitudinal stability is needed due to the fact that aircraft are designed to have an aerodynamic center of pressure (CP) located aft of the aircraft center of gravity (CG). As a result of this arrangement, cruising aircraft inherently have a nose down pitching moment, caused by the CP being aft of the CG. This nose down moment must be offset during flight by a nose up pitching moment created by the horizontal stabilizer. These opposing forces help maintain stability but create drag, which in turn reduces aircraft efficiency.
Thrust vectoring may be used to assist in the provision of aircraft longitudinal stability and the reduction of overall drag during cruising by placing the exhaust nozzle in a “nozzle up” position. When the thrust vector is directed upwards, the vertical component of the thrust vector creates a nose up pitching moment for the aircraft. The nose up pitching moment produced by the thrust vector allows the horizontal stabilizer to be operated at a lower angle-of-attack, which reduces the negative lift created by the aircraft horizontal stabilizer and therefore reduces the aircraft drag. Furthermore, integration of the thrust vectoring system into the flight control system assists in providing aircraft longitudinal stability, thus allowing highly efficient reduced-tail designs, which in turn may reduce tail weight and consequently the overall aircraft weight.
Swept-wing, T-tailed aircraft tend to suffer a marked nose up pitching moment at aerodynamic stall that can allow the low energy turbulent airflow behind the wing to immerse the tail. This can greatly reduce the effectiveness of the tail in countering the nose up pitching moment. When the nose up pitching moment created by the wing during stall is greater than the nose down pitching moment created by the horizontal tail, recovery from the stall may be impossible. Just as thrust vectoring may be used to assist the tail in providing a nose up pitching moment during cruise, thrust vectoring may be used to assist the tail in providing a nose down pitching moment during stall. All that is required is that the nozzle be placed in a nozzle-down position.
Thrust vectoring may be used further to improve landing performance and decrease or eliminate the need for thrust reversers. Landing performance is predicated on the landing approach being carried out at a generally constant angle-of-attack. At a generally constant angle-of-attack, airspeed varies directly with the weight supported by the wing i.e., aircraft weight. Required runway length is a function of aircraft weight, approach speed, and aircraft braking ability. As the ability to increase runway length and decrease aircraft weight is somewhat limited, control over aircraft stopping distance is largely exercised through control of braking ability.
Most aircraft, at landing, use thrust reversers for deceleration. However, these reversers that are used at landing for about 30 seconds can produce catastrophic events if an inadvertent deployment occurs during flight. Thrust reversers are required primarily on wet or icy runways, because of the high speeds at which aircraft are required to land. If the landing speed of an aircraft could be reduced, the need for thrust reversers could potentially be avoided.
One such method of reducing aircraft landing speed may be to provide an engine that assists in lift through adjustment of the engine thrust vector. By placing the exhaust nozzle in a nozzle-down position, some portion of the aircraft weight may be supported directly by the vertical component of the vectored thrust thus reducing the weight supported by the wing. This support of the aircraft by a vertical component of thrust vectoring could be used to reduce approach speeds, and thus reduce landing speeds. Reduced landing speeds could decrease or eliminate the need for thrust reversers on the aircraft. Induced drag would be decreased and angle-of-attack reduced.
Thrust vectoring may also be used to assist in maneuvering an aircraft. For fuselage mounted engines in particular, the left engine exhaust nozzle can be controlled to an asymmetrical vectoring position (nozzle up for example) while the exhaust nozzle of the right engine is controlled to the opposite direction (nozzle down position), and vice versa. Such thrust vectoring may be used to generate a rolling moment to the aircraft. If the thrust vectoring system is integrated into the flight control and/or auto-flight systems, then an independent backup flight control system is available to the flight crew. Furthermore, if power for the thrust vectoring system is different from the flight control system i.e., electric vs. hydraulic, then an additional level of redundancy is created, which further increases the overall safety of the aircraft. On a multi-engine aircraft, pitch axis thrust vectoring can create aircraft movement about the pitch (symmetrical vectoring) and roll (asymmetrical vectoring) axes.
Another technology related to the engine nozzle is variable area exhaust. U.S. Pat. No. 5,221,048, which is incorporated by reference herein, describes a variable exhaust area nozzle comprising a fixed structure having mounted thereon two pivoting half shells that cooperate radially and longitudinally with said fixed structure. The two shells and the fixed structure form the exhaust nozzle of the engine. Actuators are used to pivot the shells into any position between their fully opened position and their fully closed position. Although adjustment of the position of the two shells provides control over the nozzle exhaust area, it does so without modification of the engine thrust-vector angle. The apparatus described in U.S. Pat. No. 5,221,048 has no thrust vectoring capability.
Variable nozzle and thrust vectoring of the exhaust of a jet engine is known. U.S. Pat. No. 4,000,610, which is incorporated by reference herein, discloses an apparatus using a flap downstream of a series of converging-diverging flaps to provide flight maneuver (thrust) vectoring as well as external exhaust expansion control. While the series of flaps are internal to the nozzle, and are adapted to form a convergent-divergent shape, they cooperate with the one flap located downstream of the exhaust nozzle for external expansion control of the exhaust. Convergent-divergent nozzles such as this are typically used on supersonic aircraft such as military aircraft.
It would, therefore, be a significant advance in the operation of jet engines if an alternate means for providing thrust vectoring and exhaust area variation were provided. More specifically, it would be advantageous if an exhaust nozzle were provided that allowed larger angles of thrust vectoring and maintained a planar exhaust area. It would also be advantageous to provide an exhaust nozzle having a simplified design and operation for varying the angle of a thrust vector and the value of the exhaust area. Finally, it would be advantageous to provide an exhaust nozzle with actuation means that allowed for independent adjustment of the thrust vectoring angle and the nozzle exhaust area.
All references cited herein are incorporated by reference.